The underglaze was made by mixing the Zero3 white engobe with Zero3 H clear glaze (50:50) and adding 20% black stain and gum to make it paintable. The piece was bisque fired at cone 06 and the engobe formed enough glass to block the porous body below from absorbing the glaze water during dipping. Notwithstanding this, the glaze has flowed out over the underglaze because of the slight 'wet' surface it develops during the glaze firing. For dipping of the cover glaze it would be better to adjust the underglaze to melt less. This underscores the need to tune underglazes to the exact purpose. For a brushing overglaze this one would work as is.
A ceramic compound meant to be applied to green or bisque ware and covered using a transparent overglaze. There are good reasons to make your own underglazes if you are in production.